1. Technical Field
The present invention generally pertains to motor vehicles. More particularly, the present invention pertains to a feedback load control system for a vehicle equipped with power steering. More specifically, but without restriction to the particular embodiment and/or use which is shown and described for purposes of illustration, the present invention relates to a proportional, integral, derivative control system used in conjunction with a linear solenoid to provide bypass airflow when an increase in engine load by an accessory is sensed.
2. Discussion
Motor vehicles equipped with small displacement engines such as a 2.0 litre 4 cylinder engine, are highly susceptible to stalling when an accessory such as a power steering pump is operated while the engine is at idle speed. Specifically, when a vehicle operator turns the steering wheel, a demand for increased hydraulic pressure in the power steering system occurs. As the power steering pump fulfills the requirement for increased hydraulic pressure, a significant load is placed upon the engine to rotate the pump. Accordingly, without an engine control system to compensate for the increased load generated by the power steering system, the engine speed will fall, possibly stalling the engine.
Conventional control systems implement a power steering switch to signal the engine control system that the power steering system is being utilized. The switch closes once hydraulic pressure in the power steering system reaches a set point corresponding to a pressure greater than that found in the system when the steering wheel is not being turned. Once the power steering switch is closed, the engine control module is signaled to compensate for the increase in load by increasing airflow. This system has some inherent problems.
Because a certain pressure is required to trigger the power steering switch, an increase in load on the engine has already occurred. Once the switch does close, additional air begins to be delivered to the combustion chambers. However, there is a substantial time lag between the power steering switch closing and additional air entering the combustion chambers. In order to keep the engine from stalling, an amount of air capable of offsetting a full power steering load is input. This relatively large air input is required because it is not known if the sensed pressure increase was generated from a small turning of the steering wheel or a full lock. Accordingly, these systems are prone to cause excessive airflow to be introduced into the engine when the steering wheel is rocked even slightly, thereby causing the engine speed to flare upward.
Another known issue associated with the use of power steering system pressure switches arises in cold weather operation. Conventional systems utilizing a power steering switch to sense an increase in pressure are subject to false triggers of the switch based on an increase in viscosity of the cold power steering fluid.